When configuring the Document Generation action, the configuration indicates the document quota has been exceeded, even when no documents have been created.
Even if both assets are created and live, if they're on separate Salesforce contracts, Document Generation for Office 365 will not work.
This is caused by a mismatch in the licensing with the associated customer account.
Looking at the JSON call that is made when the action configuration loads, you will see the following inside of developer tools:
{"Total":0,"Used":0,"IsTrial":false,"SubscriptionStartDate":"0001-01-01T00:00:00","SubscriptionEndDate":"0001-01-01T00:00:00","OverUsage":0,"QuotaOverageAllowance":0,"ErrorType":400,"IsSuccess":false,"ErrorPayload":null,"Info":null,"SubscriptionEndDateString":"01 Jan 0001"}